Medical infusion pumps serve the needs of patients receiving intravenous, intramuscular or similar pharmaceutical therapy by delivering controlled amounts of fluid under pressurized flow conditions to the patients. Infusion pumps provide the additional advantage of being portable, allowing the patient to carry on normal activities while still maintaining his or her intravenous fluid administration regiment.
Infusion systems generally draw fluid from reservoirs through tubing. Additional segments of tubing are used to deliver the fluid from the infusion pump to the patient. Ideally, a continuous section of tubing extending from the fluid reservoir to the delivery needle is used to insure sterility.
If the tubing becomes occluded or partially occluded, the patient may be subject to an "under delivery" or "no delivery" situation. The problem of occlusion detection is further complicated in that many patients maintain and operate their own fluid administration regiment without the supervision of health care providers. Therefore, detecting occlusions in the fluid lines is important for safe and effective operation of the infusion pumps.
Occlusions may be of two kinds, upstream and downstream of the pump. Each has its own set of indications. Upstream occlusions may be detected by an upstream sensor monitoring pressure drop in the upstream tubing. In such situations, the "pull" of the infusion pump against the occlusion will produce up to a -10 psi pressure drop or partial vacuum relative to a baseline pressure of the system, the baseline being defined, and for the purposes of this invention is defined, as the system pressure present between pumping cycles when the system is operating in an unoccluded condition. This phenomenon has led to the technique disclosed in U.S. Pat. No. 5,096,385 (the '385 patent) to measure upstream occlusions in connection with a peristaltic infusion system.
In particular, the '385 patent discloses use of a downstream pressure sensor to detect negative going pressure transients and identify upstream occlusions in the peristaltic system. The normal pressure curve created by the peristaltic action of this system is the result of the wave-like motion of pump "fingers" and exhibits no pressure drops as the fluid is pressurized and propelled to the patient. The detection method of the '385 patent appears to require sensing detection of small pressure changes, e.g., as little about 0.6 psi and cannot be applied to situations where the normal pumping cycle exhibits transient pressure drops. Moreover, irrespective of the placement of the sensor, it is commonly not possible to accurately measure this degree of change when detecting across a tube wall. This kind of measurement typically requires insertion of a sensor in the fluid path or operation of a sensor across a flexible membrane adjacent to the fluid path. Both of these options present risks to the sterility of the fluid being infused, a problem that is further complicated where a patient is maintaining his/her own infusion regimen. Sensors in the fluid path would have to be either disposable or re-sterilizeable. Membrane type sensors require a disposable tubing set specific to the sensor.
Downstream occlusions may be detected by a downstream sensor monitoring pressure change in the downstream line. U.S. Pat. No. 4,526,574, for example, discloses measuring an initial tube wall deflection or pressure to determine a fixed baseline value (pre-pumping cycle pressure) at the beginning of the infusion process. Subsequent measurement must be within a predetermined range relative to the fixed baseline value, or an alarm will sound. Additionally, the '574 patent fails to consider the variations that occur in the system over its running time and fails to account for elevated pressure resulting from overfilled medication containers.
Therefore there is a need to develop an improved system and method for detection of up and downstream occlusions. The system and method would operate by pressure detection directly through infusion tubing walls and account for pressure variability resulting from the infusion system, the tubing and the patient. An additional need is the development of an accurate system that avoids compromise of infusion fluid sterility.